1. Field of the Invention
The present invention generally relates to heat treatment apparatuses and more particularly to a heat treatment apparatus which performs an anneal process or a chemical vapor deposition (CVD) process by heating an object to be processed, such as a single crystalline substrate or a glass substrate, with a lamp and a quartz window used for such a heat treatment apparatus. The present invention is suitable for a rapid thermal processing (RTP: Rapid Thermal Processing) used for manufacturing semiconductor devices, such as a memory or an integrated circuit (IC). The rapid thermal processing (RTP) includes rapid thermal annealing (RTA), rapid thermal cleaning (RTC), rapid thermal chemical vapor deposition (RTCVD), rapid thermal oxidization (RTO) and rapid thermal nitriding (RTN).
2. Description of Related Art
There is a single wafer heat treatment apparatus as one of semiconductor manufacturing apparatuses, which performs an annealing process or a CVD process by heating a semiconductor wafer (hereinafter simply referred to as a wafer) with a heat radiation lamp.
FIG. 1 shows an example of a conventional heat treatment apparatus. The heat treatment apparatus shown in FIG. 1 comprises a process chamber 11, a placement stage 12 on which a wafer W is placed and a heat radiation lamp 14. The placement stage 12 having a ring-like shape is provided in the process chamber 11, and is rotatable about the vertical axis thereof.
The heat radiation lamp 14 is arranged so as to opposite to the placement stage 12 with a light-transmitting window 13 formed of a quartz made flat plate. The placement stage 12 supports the peripheral edge of the wafer W from a lower part side. The wafer W is heated at a predetermined temperature while supplying a process gas from a side wall of one side of the process chamber 11 and exhausting from the side wall of another side. It should be noted that a rotation mechanism to rotate the placement stage 12 maintains airtightness of the process chamber 11 by using a magnetic coupling. The rotation mechanism is illustratively shown in FIG. 1.
The placement stage 12 is formed of a material having a superior heat-resistance so that the placement stage 12 is not transformed at a processing temperature of about 1000xc2x0 C. SiC (silicon carbide) is used as such a material.
In the above-mentioned heat treatment apparatus, both the placement stage 12 and the wafer W are heated with the heat radiation lamp 14 from an upper part side. When the placement stage 12 is formed by SiC, the temperature rise of the placement stage 12 is slower than that of the wafer W since the heat capacity of SiC is larger than Si (silicone) which forms the wafer W.
For this reason, at the time of heating the wafer W, the temperature of the placement stage 12 is lower than the temperature of the wafer W. Therefore, heat of the circumferential edge of the wafer W transmits to the placement stage 12, and, thus, the temperature of the circumferential edge of the wafer W becomes lower than the temperature of the central part thereof. Consequently, a temperature distribution is generated in the surface of the wafer W.
On the other hand, heating of the wafer W at a temperature higher than about 800xc2x0 C. generates a crystal defect referred to as a slip in the wafer W. The slip is easily generated as a temperature difference within the surface of the wafer W increases.
Therefore, in the conventional equipment, the wafer W cannot be heated at a high rate so that a delay in raising the temperature of the placement stage 12 does not become large, that is, the temperature difference within the surface of the wafer W is maintained small. This is one of causes that prevents improvement in a throughput. As for measures to solve the problem, it can be considered to increase an amount of heat radiation on the side of the periphery of the wafer W, such a method is difficult to realize since it is difficult to increase directivity of the heat radiation lamp 14 due to its construction.
Irradiation areas corresponding to a plurality of heat radiation lamps 14 are formed on the wafer W. A distance between the heat radiation lamp 14 and the wafer W cannot be made small from the point such as reservation of a conveyance area. For this reason, the directivity of each heat radiation lamp 14 is bad. Specifically, the directivity of a unit which is formed by combining a single heat radiation lamp and a reflector is bad. That is, a plurality of irradiation areas overlap with each other and the overlapping area between the irradiation areas is large since each above-mentioned irradiation domain spreads.
A plurality of probes of the radiation thermometer (not shown) is arranged at a plurality of positions, respectively, underneath the wafer W. The magnitude of heat dissipation from the wafer W differ from the position at which the probe of the radiation thermometer is arranged to position at which the probe is not arranged. Therefore, in order to heat the wafer W uniformly over the whole surface, it is necessary to adjust the illumination distribution by the light (radiation heat) from the lamp 14 on the wafer W. However, if the above-mentioned overlapping area between the irradiation areas is large, adjustment of an illumination distribution is difficult.
Additionally, in order to manufacture a semiconductor integrated circuit, various kinds of heat treatment, such as a film deposition process, an anneal process, an oxidization diffusion process, a sputtering process, an etching process and a nitriding processing may be repeatedly performed on a silicon wafer a plurality of times to silicone boards. Since yield rate and quality of semiconductor manufacturing processes can be improved, the RTP technology to rise and drop the temperature of the wafer (object to he processed) has attracted attention. A conventional RTP apparatus generally comprises: a single-wafer chamber (process chamber) for accommodating an object to be processed (for example, a semiconductor wafer, a glass substrate for photograph masks, a glass substrate for a liquid-crystal display or a substrate for optical discs); a reflector (reflective board) arranged at the opposite side of the object to be processed with respect to a quartz window arranged in the interior of the process chamber; and a heating lamp (for example, halogen lamp) arranged at an upper part or above the quartz window, and the lamp.
The reflector is made of aluminum, and gold plating is given to a reflective part thereof. A cooling mechanism such as a cooling pipe is provided so as to prevent temperature breakage of the reflector (for example, exfoliation of gold plating due to a high temperature). The cooling mechanism. is provided so as to prevent the reflector from being an obstacle of cooling the object to be processed at the time of cooling. The rapid temperature rising demanded for the RTP technology is dependent on the directivity of the optical irradiation to the object to be processed and the power density of the lamp.
FIG. 2 is an illustration showing an arrangement of a single end lamp and a reflector. As shown in FIG. 2, the directivity with respect to the object to be processed arranged underneath the single end lamp 15 having only one electrode part 16 and the energy efficiency of the lamp 15 is maximum when a degree of an angle a of inclination of the reflector 17 relative to the lamp 15 is set to 45 degrees.
The quartz window may be in the shape of a board, or can be in the form of tube which can accommodate the object to be processed. When maintaining a negative pressure environment in the process chamber by evacuating gasses in the process chamber by a vacuum pump, a thickness of the quartz window is set to, for example, about 30 to 40 mm so as to maintain the pressure difference between the internal pressure and the atmospheric pressure. The quartz window may be formed in a curved shape having a reduced thickness so as to prevent generation of a thermal stress due to temperature difference generated by a temperature rise.
A plurality of halogen lamps are arranged so as to uniformly heat the object to be processed. The reflector reflects the infrared rays irradiated from the halogen lamps toward the object to be processed. The process chamber is typically provided with a gate valve on a sidewall thereof so as to carry in and out the object to be processed. Moreover, a gas supply nozzle, which introduces a process gas used for heat treatment, is connected to the sidewall of the process chamber.
The temperature of the object to be processed affects the quality of process such as, for example, a thickness of a film in a film deposition process, etc. For this reason, it is necessary to know the correct temperature of the object to be processed. In order to attain high-speed heating and high-speed cooling, a temperature measuring device which measures the temperature of the object to be processed is provided in the process chamber. The temperature measuring device may be constituted by a thermocouple. However, since it is necessary to bring the thermocouple into contact with the object to be processed, there is a possibility that the processed body is polluted with the metal which constitutes the thermocouple. Therefore, there is proposed a payro meter as a temperature measuring device which detects an infrared intensity emitted and computes a temperature of an object to be processed from the back side thereof based on the detected infrared intensity. The payro meter computes the temperature of the object to be processed by carrying out a temperature conversion by an emissivity of the object to be processed according to the following expression:
Em(T)=xcex5EBB(T)xe2x80x83xe2x80x83(1)
where, EBB(T) expresses a radiation intensity from a black body having the temperature T; Em(T) expresses a radiation intensity measured from the object to be processed having the temperature T; xcex5 epsilon expresses a rate of radiation of the object to be processed.
In operation, the object to be processed is introduced into the process chamber through the gate valve. The peripheral portion of the object to be processed is supported by a holder. At the time of heat treatment, process gases such as nitrogen gas and oxygen gas, are introduced into the process chamber through the gas supply nozzle. On the other hand, the infrared ray irradiated from the halogen lamps is absorbed by the object to be processed, thereby, rising the temperature of the object to be processed. However, the thickness of the conventional quartz window is as thick as several 10 mm. For this reason, there are the following problems.
First, the lamp light is absorbed by quartz, which reduces the irradiation efficiency to the object to be processed. Second, since a difference in temperature arises between a lamp side and its opposite side at the time of rapid temperature rising such as in RTP, the quartz window may be damaged due to difference in the thermal stress between the front side and back side of the quartz window. Third, if the lamp is curved similar to the quartz window, a distance between the object to be processed and the lamp is increased, which deteriorates the directivity of the lamp. Fourth, when the temperature of the quartz window rises, a deposition film or a byproduct may be formed on the surface of the quartz window especially when a film deposition process is performed, and, thus, a temperature repeatability cannot be maintained and the number of cleaning operations applied to a process chamber is increased.
On the other hand, absorption of the lamp light by the quartz window can be decreased by decreasing its thickness. However, if the thickness of the quartz window decreases, the quartz window cannot withstand the pressure difference between the negative pressure inside the process chamber and an atmospheric pressure and the quartz window may easily be destroyed. Thus, there is a problem in that the quartz window having a reduced thickness cannot be used for a process chamber which forms a negative pressure therein. Further, since the radiation light form a heat source is introduced into the object to be processed while being diffused, the directivity of the radiation light is not sufficient, and there is a demand for improving the directivity.
It is a general object of the present invention to provide an improved and useful quartz window and heat treatment apparatus in which the above-mentioned problems are solved.
A more specific object of the present invention is to provide a quartz window which can decrease an amount of absorption of heat from a heat source while maintaining a pressure difference between the pressure inside a process chamber and an atmospheric pressure.
Another object of the present invention is to heat an object to be processed with heat radiation lamps with less temperature difference within an entire surface of an object to be processed.
A further object of the present invention is to improve a directivity of a heat radiation lamp so as to achieve easy adjustment of the illumination distribution on the object to be processed.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a heat treatment apparatus comprising: a process chamber which defines a process space for processing an object to be processes; a placement stage provided in the process chamber so as to place the object to be processed thereon; a gas supply part which supplies to the process chamber a process gas for processing the object to be processed; a light-transmitting window provided as a part of the process chamber so that the light-transmitting window is opposite to the object to be processed placed on the placement stage; and a heating unit which comprises a heat radiation lamp provided on an opposite side of the process chamber with respect to the light-transmitting window, wherein the light-transmitting window constitutes a convex lens part which is formed on a periphery of the light-transmitting window and protrudes into the process space.
According to the present invention, a light traveling from the heat radiation lamp toward outside of the object to be processed is deflected toward inside by the convex lens part. Thus, heat radiation energy emitted by the heat radiation lamp can be efficiently used. Additionally, if a temperature rising rate is increased when heating the object to be processed, uniformity within the surface of the object to be processed can be maintained high. In a case in which the object to be processed is a silicon wafer, generation of a slip, which is a crystal defect, can be prevented.
In the heat treatment apparatus according to the present invention, the placement stage may support a periphery of the object to be processed. Additionally, the placement stage may have a heat capacity greater than that of the object to be processed. In one embodiment, the object to be processed may be a silicon wafer and said placement stage is made of silicon carbide. The heat radiation lamp may be located at a focal point of the convex lens part. Further, the placement stage may be rotatable relative to the heat radiation lamp about a vertical axis thereof.
Additionally, there is provided according to another aspect of the present invention a heat treatment apparatus comprising: a process chamber which defines a process space for processing an object to be processes; a placement stage provided in the process chamber so as to place the object to be processed thereon; a gas supply part which supplies to the process chamber a process gas for processing the object to be processed; a light-transmitting window provided as a part of said process chamber so that the light-transmitting window is opposite to the object to be processed placed on the placement stage; and a heating unit which comprises a plurality of heat radiation lamps provided on an opposite side of the process chamber with respect to the light-transmitting window, wherein the light-transmitting window constitutes a plurality of convex lens parts each of which corresponds to a respective one of the heat radiation lamps and protrudes into the process space.
According to this invention, since the irradiation area of each of the heat radiation lamps is narrowed by the convex lens part, the directivity of the heat radiation lamps is improved, and easy adjustment of the luminescence distribution on the object to be processed is achieved.
In the above mentioned heat treatment apparatus according to the present invention, each of the heat radiation lamps may be located at a focal point of a respective one of the convex lens parts. Additionally, the placement stage may be rotatable relative to the heat radiation lamps about a vertical axis thereof. In one embodiment of the present invention, each of the heat radiation lamps may has an arc shape, and the heat radiation lamps may be concentrically arranged in the heating unit. In another embodiment, each of the heat radiation lamps may be a single end type, and the heat radiation lamps may be provided in the heating unit in an island arrangement. In still another embodiment, each of the heat radiation lamps may have a rectilinear shape, and the heat radiation lamps may be arranged parallel to each other in the heating unit.
Additionally, there is provided according to another aspect of the present invention a heat treatment apparatus comprising: a process chamber in which a heat treatment is applied to an object to be processed; a heat source which heats the objects to be processed by irradiating a radiation light onto the object to be processed; and a quartz window provided between the object to be processed and the heat source, the quartz window comprising: a plate made of quartz; and a lens part fixed to the plate so as to improve a directivity of the radiation light emitted by the heat source and increase a mechanical strength of the plate.
According to the above-mentioned invention, the quartz window has a reduced thickness with a sufficient strength since the lens part reinforces the plate. Accordingly, an amount of heat from the heat source absorbed by quartz window can be reduced. Additionally, since the lens part converges the radiation light emitted from the heat source, the directivity of the radiation light irradiated onto the object to be processed is improved. The heat treatment apparatus having the quarts window according to the present invention is suitable for a heat treatment performed under a negative pressure environment in which a load due to a pressure difference is applied to the quartz window.
In the heat treatment apparatus according to the present invention, the heat source may have plurality of lamps, and the lens part may have a plurality of lens elements corresponding to the lamps. Each of the lens element improves the directivity of the radiation light emitted by a respective one of the lamps. Additionally, the lens part may be provided on a surface of the plate facing the object to be processed. The lens part may be provided on both a surface of the plate facing the object to be processed and a surface opposite to the surface facing the object to be processed.
Additionally, the plate of the quartz window may have at least one reinforcing member which increases a strength of said plate. Accordingly, the thickness of quartz plate can be further reduced, thereby decreasing an amount radiation light absorbed by the quartz plate. The thickness of the plate of the quartz window is preferably equal to or less than 7 mm. More preferably, the thickness of the plate of the quartz window is equal to or less than 5 mm. The reinforcing member may made of aluminum.
Additionally, the heat treatment apparatus according to the present invention may further comprise a cooling arrangement which cools said reinforcing member so as to prevent the reinforcing member and the plate from being thermally deformed. The lens part may be provided on a first surface of the plate, and at least one reinforcing member may be provided on a second surface of said plate opposite to the first surface so as to increase a strength of the plate.
Further, a plurality of reinforcing members may be provided on the plate, and at least one waveguiding part made of quartz may be provided between adjacent reinforcing members, the waveguiding part transmitting the radiation light passed through said lens part and said plate toward the object to be processed. According to the difference in refraction index between quartz and air or vacuum, a total reflection occurs within the waveguiding part. Thus, the radiation light can be efficiently directed toward the object to be processed by being passed through the waveguiding part.
Additionally, the heat treatment apparatus according to the present invention may further comprise an exhaust device connected to the process chamber so as to maintain a negative pressure inside said process chamber.
Additionally, there is provided according to another aspect of the present invention a quartz window configured to be incorporated into a heat treatment apparatus which applies a heat treatment to an object to be processed by a radiation light emitted by a heat source, the quartz window being arranged between the object to be processed and the heat source, the quartz window comprising: a plate made of quartz; and a lens part fixed to said plate so as to converge the radiation light emitted by the heat source toward the object to be processed and increase a mechanical strength of the plate.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.